Autonomous robots that perform household functions such as floor cleaning and lawn cutting are now readily available consumer products. Commercially successful robots are not unnecessarily complex, and generally operate randomly within a confined area. In the case of floor cleaning, such robots are generally confined within (i) touched walls and other obstacles within the rooms of a dwelling, (ii) IR-detected staircases (cliffs) down; and/or (iii) user placed detectable barriers such as directed IR beams, physical barriers or magnetic tape. Other robots map the dwelling using a complex system of sensors and/or active or passive beacons (e.g., sonar, RFID or bar code detection, or various kinds of machine vision).
Some consumer robotic lawn mowers use a similar “invisible” barrier—a continuous guide conductor boundary (e.g., a boundary wire) for confining random motion robotic mowers. The boundary wire is intended to confine the robot within the lawn or other appropriate area, so as to avoid damaging non-grassy areas of the yard or intruding onto a neighboring property. Some consumer robotic lawn mowers use localization systems that make use of triangulation to determine the robot position within the boundary. For example, multiple beacons are positioned around the property to be mowed. Signals sent between the beacons and the lawnmower positioned in the property allow the lawnmower to estimate the angles and the distance by calculating time-of-flight to each of the beacons, and using trigonometry to calculate the robot's current position. In another example, the system can triangulate the distance to an object using a fixed-angle laser pointer and a CMOS imager, with a baseline between the two. In such examples, the pixel location of the received signal at the imager is indicative of the distance to the object.
There are several challenges in determining the position of an outdoor robot within a barrier. The resolution of current commercially available GPS applications is inadequate for this application (e.g., resolution is insufficient to prevent the lawnmower from not mowing a flower bed or other “no-mow” zone), particularly in light of tree cover commonly found in lawns. The variation in terrain also makes it difficult for the robot to “see” boundary markers; tilt or slant in the lawn can cause a moving mower having a sweeping beacon detector to not engage, or miss, a beacon. The additional costs and power requirements to improve these factors are important for consumers.